In most internal combustion engines, it is desirable to maintain the pressure within the crankcase at a level equal to or slightly less than atmospheric pressure to reduce leaks through gaskets and seals from the crankcase to the atmosphere. As is well known, in an internal combustion engine, so-called blow-by gases are emitted in the crankcase as a result of leaks of the air-fuel intake mixture and combustion gases through the clearances around piston rings during the compression, combustion and/or exhaust cycles. Because of these blow-by gases, the internal crankcase pressure will inherently rise promoting oil leakage from the crankcase to the surrounding environment.
Traditionally, excess crankcase pressure was vented to the atmosphere through a breather port to solve this problem. More recently, environmental considerations have dictated that the blow-by gases in the crankcase not be released to the atmosphere untreated. One method of dealing with blow-by gases in an environmentally acceptable manner vents these gases back to the combustion chamber. Such closed crankcase ventilation (CCV) systems recycle the blow-by gases by burning these gases together with the air-fuel intake mixture, thereby preventing the direct release of oil, uncombusted fuel and other pollutants to the environment.
Many heavy duty and high horsepower engines use a turbocharger or supercharger to increase the power output of the engine. In such an engine, the fresh air intake is pressurized before entering the combustion chamber, thereby allowing the combustion of more fuel and producing more power for a given engine volume. This design creates difficulties for CCV systems as the lower pressure blow-by gases cannot be introduced directly into the higher pressure intake air line. One possible solution to this problem is to introduce the blow-by gases upstream of the turbocharger prior to pressurization of the intake air. This method is unsatisfactory, however, as particulate contaminants in the blow-by gases such as oil droplets and partially combusted hydrocarbons can lead to pitting and fouling of the turbocharger.